Can I be a monk in Freeport or a necromancer in Qeynos?
No. To be a monk, you must be a Qeynos citizen. To be a necromancer, you must be a Freeport citizen. While any race can play any class, some of them must betray their home city before they may take up residence in a new town. All races have the option to change their citizenship through the betrayal quest, but the majority of subclasses are specific to one city or the other.
